An exhaust gas containing silane (SiH4) or the like is discharged from manufacturing apparatuses of semiconductor devices or liquid crystal panels. Since silane is a harmful and combustible gas, the exhaust gas from these manufacturing apparatuses cannot be released to the atmosphere as it is. Therefore, it has been customary to introduce the exhaust gas into a treatment system where silane contained in the exhaust gas is oxidized and decomposed to be made harmless.
As this type of treatment system, as disclosed in Japanese laid-open patent publication No. 2003-251130, there has been known a system which has a combustion treatment unit for treating an exhaust gas by combustion and a gas cleaning unit for removing a by-product produced in this combustion treatment unit from the exhaust gas. The exhaust gas is first introduced into the combustion treatment unit where silane in the exhaust gas is oxidatively decomposed by flames generated in the combustion treatment unit. By oxidatively decomposing silane, SiO2 (Silica) is produced as a by-product. Then, the exhaust gas is introduced into the gas cleaning unit where the by-product in the exhaust gas is removed. In the system disclosed in the above patent document, a fan scrubber is used as the gas cleaning unit. This fan scrubber causes gas-liquid contact by rotating an impeller while supplying water in a casing, thereby removing the by-product from the exhaust gas.
The Japanese laid-open patent publication No. 2001-293335 discloses a treatment system for treating fluorine compounds (NF3, ClF3, SF6, CHF3, C2F6, Cf4) contained in an exhaust gas discharged from a semiconductor device fabrication system (especially, dry etching apparatuses) by using a catalyst layer. In this treatment system, a spray-type gas cleaning apparatus (water spray tower) is disposed upstream of the catalyst layer and this water spray tower cleans the exhaust gas and removes fine dust such as silica or the like contained in the exhaust gas.
The dust existing in the above-mentioned exhaust gas is extremely minute and some of the dust has a diameter of less than 1 μm. The fan scrubber is known as a gas cleaning apparatus capable of removing fine dust at high efficiency. However, the fan scrubber has a more complicated structure than a spray-type gas cleaning apparatus and is expensive. Further, the fan scrubber needs electric power because a motor is used as a drive source of an impeller and has higher running cost. On the other hand, in the spray-type gas cleaning apparatus, it is difficult to remove submicron-order fine dust and dust removal efficiency is low.